From c498c1d09ad99605ac34d4236102e4434937bb5b Mon Sep 17 00:00:00 2001
From: afonsofrancof <afonso@francof.net>
Date: Thu, 22 Feb 2024 02:46:32 +0000
Subject: [PATCH] [c] Implemented the chacha20_int_attck.c

---
 TPs/TP02/c/src/chacha20_int_attck.c | 80 +++++++++++++++++++++++++++++
 1 file changed, 80 insertions(+)
 create mode 100644 TPs/TP02/c/src/chacha20_int_attck.c

diff --git a/TPs/TP02/c/src/chacha20_int_attck.c b/TPs/TP02/c/src/chacha20_int_attck.c
new file mode 100644
index 0000000..fd4ce1c
--- /dev/null
+++ b/TPs/TP02/c/src/chacha20_int_attck.c
@@ -0,0 +1,80 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+void attack(char *fctxt, int pos, char *plain_at_pos, char *new_plain_at_pos) {
+	FILE *f = fopen(fctxt, "rb");
+    if (f == NULL) {
+        fprintf(stderr, "Error opening file\n");
+        return;
+    }
+
+	// Get the size of the file
+	fseek(f, 0, SEEK_END);
+	unsigned long fsize = ftell(f);
+    rewind(f);
+
+	// Allocate memory for the file
+	unsigned char *nonce_and_ciphertext = malloc(fsize * sizeof(unsigned char));
+	if (nonce_and_ciphertext == NULL) {
+		printf("Error allocating memory\n");
+		fclose(f);
+		return;
+	}
+
+	if (fread(nonce_and_ciphertext, 1, fsize, f) != fsize) {
+		printf("Error reading file\n");
+		fclose(f);
+		free(nonce_and_ciphertext);
+		return;
+	}
+	fclose(f);
+
+	unsigned char *ciphertext = malloc((fsize * sizeof(unsigned char)) - 16);
+	memcpy(ciphertext, nonce_and_ciphertext + 16, fsize - 16);
+
+    int plain_at_pos_len = strlen(plain_at_pos);
+    // Modify the ciphertext
+    for (int i = 0; i < plain_at_pos_len; i++) {
+        ciphertext[pos + i] = ciphertext[pos + i] ^ (plain_at_pos[i] ^ new_plain_at_pos[i]);
+    }
+    memcpy(nonce_and_ciphertext + 16, ciphertext, fsize - 16);
+
+    // Write the modified ciphertext to the file
+    char *output_file = malloc(strlen(fctxt) + 7);
+    strcpy(output_file, fctxt);
+    strcat(output_file, ".attck");
+    FILE *foutput = fopen(output_file, "wb");
+
+    if (foutput == NULL) {
+        fprintf(stderr, "Error opening output file\n");
+        fclose(f);
+        free(ciphertext);
+        free(output_file);
+        return;
+    }
+
+    if (fwrite(nonce_and_ciphertext, 1, fsize, foutput) != fsize) {
+        fprintf(stderr, "Error writing to file\n");
+        fclose(f);
+        fclose(foutput);
+        free(ciphertext);
+        free(output_file);
+        return;
+    }
+
+    fclose(f);
+    fclose(foutput);
+    free(ciphertext);
+    free(output_file);
+}
+
+int main(int argc, char *argv[]) {
+    if (argc != 5) {
+        fprintf(stderr, "Usage: %s <fctxt> <pos> <ptxtAtPos> <newPtxtAtPos>\n", argv[0]);
+        return 1;
+    }
+
+    attack(argv[1], atoi(argv[2]), argv[3], argv[4]);
+    return 0;
+}